A Trial of Spraying Nitrate Fertiliser on Hazelnut Suckers in Canterbury

Peter Barrowclough 31 March 2025

At a Hazelnut Growers Association Field Day on 22nd June last year, Assoc Prof Clive Kaiser from Lincoln University told us that he had recently seen overseas the use of nitrate fertiliser to “burn” suckers off, achieving good sucker control.

I decided to experiment with this option.  I have around 2500 whiteheart trees in Canterbury on good soils with irrigation.  They are 17 years old.

I purchased a 20kg bag of 27% Calcium Ammonium Nitrate (CAN) from Farmlands.  I made up a 17% solution in 120 litres of water and sprayed it on my suckers on the 11th of Nov.  It was not very soluble and gummed up my sprayer.  This took about an hour to clean out afterwards.  But I did manage to get the spray on half of my orchard or around 1250 trees. The remaining half of the orchard was sprayed with Buster at my normal rates.  The  CAN appeared to be quite fast in acting and the suckers showed wilting within a day.  I was encouraged.

Early wilting of suckers sprayed with CAN.

However the suckers sprayed with CAN recovered and required a second spray whereas the suckers sprayed with Buster did not.

I was wary of using CAN again because of its insolubleness so I purchased Sulphate of Ammonia.  I made up a 10% solution and sprayed it on the suckers for the same half of the orchard I had tried the CAN on the 30th of Nov.  It was much more soluble and the sprayer did not require cleaning out.

I also sprayed the remainder of the orchard again with Buster on the 7th of Dec to get a fair comparison.

We took an overseas trip during December and I was out of the country for a month.  It was a very wet period with frequent rain giving good conditions for strong sucker growth.

I came back to strong sucker growth on the trees sprayed with  sulphate of ammonia which were now reaching up into the canopy.  Control for the Buster sprayed suckers was better, but not complete.  

Strong regrowth after a month for suckers sprayed with Sulphate of ammonia
Better control for suckers sprayed with Buster during the same time period.

Conclusions.

For those of you that grow Whiteheart you will know that they are prolific suckering trees.  While it would be preferable to control them with a fertiliser rather than an agrichemical, this limited trial would indicate more frequent applications may be needed, or more research done.  Sucker control is a major issue and once they reach up into the canopy they can no longer be sprayed without impacting the tree.  Suckers can then grow up into the top of the canopy restricting light and thus nut formation.  I will be returning to my regular use of Buster for control.